On Sunday, skywatchers will be treated to a rare celestial event when a supermoon and a blood moon coincide for the first time in over 30 years. It will last for more than an hour and will be visible throughout much of the world, and can be streamed online.

Supermoon is a popular term used to describe when a full moon occurs at the point in the lunar orbit when the moon is closest to Earth. Astronomers refer to this point in the lunar orbit as perigee. The full moon at perigee can appear up to 14 percent larger than it would at apogee, the point in the lunar orbit when the moon is farthest from Earth.

Supermoons are rare celestial events in and of themselves. However, for a supermoon to coincide with a total lunar eclipse is exceedingly rare. The last time a supermoon lunar eclipse occurred was in 1982 and the next time you’ll be able to see one is in 2033.

A total lunar eclipse, on the other hand, can only occur during a full moon when the moon passes into Earth’s umbra, or shadow, forming an alignment with the Earth and the sun known as syzygy. The Earth obstructs sunlight, preventing it from reaching the moon directly. However, the moon does not completely disappear from view. Instead, the moon will turn blood red, the result of sunlight scattering off of Earth’s atmosphere. Total lunar eclipses are sometimes referred to as blood moons due to the reddish glow they give off.

This visualization shows Earth as it would appear from the surface of the moon during the total lunar eclipse on April 15, 2014. Image Credit: NASA Scientific Visualization Studio

However, being a supermoon and blood moon are not the only things that make this celestial event special. This full moon is also what is known as a Harvest Moon, a term historically given to the full moon that occurs closest to the autumnal equinox. In addition, this lunar eclipse completes what is called a lunar tetrad, a sequence of four total lunar eclipses each separated by six lunar months.

A supermoon lunar eclipse is an event that occurs only a few times in a person’s life. There were only five over the course of the entire 20th century. NASA and the Slooh Community Observatory will be providing live streams of this rare celestial event for those who are unable to view it where they live or due to poor weather conditions. NASA and Slooh’s live streams begin at 8 p.m. EDT on Sunday, Sept. 27, 2015.